Created attachment 135740 [details] image showing the issue Application icon added to panel is too small; panel space is visible underused. STEPS TO REPRODUCE 1. Make sure that panel height is 36 (default) 2. Add an application icon to panel (ex: menu, right click on app and "Add to panel (Widget)") OBSERVED RESULT icon is too small and does not fill available panel space EXPECTED RESULT icon is normal and fill panel space properly SOFTWARE/OS VERSIONS Operating System: openSUSE Tumbleweed 20210205 KDE Plasma Version: 5.20.5 KDE Frameworks Version: 5.78.0 Qt Version: 5.15.2 Kernel Version: 5.10.12-1-default OS Type: 64-bit ADDITIONAL INFORMATION - please see attached plasma5205h36small.png - if panel height is increased to 40 than icon looks good (please see attached plasma5205h40ok.png) - in Plasma 5.18.6 it worked as expected (please see attached plasma5186h36ok.png) - I do not know when this issue appeared because I used a theme where it did not manifested but I suspect since Icon-only Task Manager was made default
Created attachment 135741 [details] panel height 40 works
Created attachment 135742 [details] no problem in plasma 5.18.6
The margins are smaller in Plasma 5.21.
Created attachment 135861 [details] small icons kde neon plasma 5.2.1
Tested with Plasma 5.21 on both openSUSE Tumbleweed and KDE Neon and bug is not fixed. Deleted ~/.cache/icon-cache.kcache without effect. Please see attached kdeneon_plasma521.png
Looking deeper, this was an intentional change with the goal of using consistent margins for everything in the panel. Your "before" screenshots show differing margins between the applets and task manager icons on the left, from the system tray and clock on the right. The "After" screenshots depict consistent margins. One consequence of this is that the applets and task manager icons had to get smaller. If you don't like it, you can adjust your panel size, use Icon applets instead of pinned task manager apps, or complain to Niccolò about it. :)